Pulse propagation.

		*  -------- |4>
		*    \        
		*     \ E3    -------- |3>  
		*      \       /    \
		*       \  E2 /      \ 
		*        \   /        \ E1
		*       ------- |2>    \
		*                       \
		*                    ------- |1>

Probe field only, the probe absorbed on a short distance
./Nlevels_no_dopler_with_z.run  --E2o 0.0 --E3o 0.0

Slow light
./Nlevels_no_dopler_with_z.run  --E2o 6.0 --E3o 0.0

N-laser-system is on, probe field (E1) absorbed at short distance, 
very similar to just the probe fielf on
./Nlevels_no_dopler_with_z.run --E2o 6.0 --E3o 10.0